An IGBT (Insulated Gate Bipolar Transistor) is a power semiconductor element that can perform on-off control of a high voltage or a large current. A package in which the IGBT and a freewheel diode for a load current are combined into a circuit, is called as an IGBT module and is used as an elementary component for configuring an inverter circuit or the like.
A power module in which the IGBT module and a printed circuit board on which control circuits such as a driving circuit for the IGBT and a protective circuit are formed are packaged, is called as an IPM (Intelligent Power Module). Because of improvement in convenience and reliability due to built-in control circuits, the power module is widely used for an inverter device or the like.
In order to configure three-phase inverter circuitry, power modules are generally configured as a package called “6-in-1” in which six IGBTs and six diodes are equipped, or as a package called “7-in-1” in which an IGBT and a diode are further added to configure a braking circuit.
As described above, it is general that a power module is equipped with a plurality of IGBTs. In a case where the power modules are used in an inverter circuit, individual IGBTs have different electric potentials; therefore, a relay terminal connected to an IGBT has an electric potential different from that of a relay terminal connected to another IGBT. This leads to a requirement that insulation between the relay terminals is ensured. As the power modules are further downsized or adapted to a higher voltage, it becomes difficult to ensure creepage distances between the relay terminals or space distances therebetween.
In relation to ensuring insulation performance of power modules, Japan Electrical Manufacture's Association (JEM standards) in Japan, or International Electrotechnical Commission (IEC standards) or the like in foreign countries stipulates a creepage distance and space distance which are to be guidelines necessary for insulation in environments in which to use the modules, an applied voltage, or the like.
In a conventional power module, in order to ensure a space distance and creepage distance between parts implemented on a printed circuit board, a structure is adopted in which the printed circuit board is provided with a slit into which a dielectric shielding plate is inserted (for example, refer to Patent Document 1). In the structure, the creepage distance is ensured by the slit, and the space distance is ensured by the shielding plate, which thereby allows inter-parts distances to be shorter than a stipulated distance.